Developing solid-state emitters (e.g., lasers) that emit radiation in the ultraviolet (UV) range presents a challenging engineering problem. Factors limiting the performance of such devices include the efficiency in p-type doping and carrier injection, as well as material quality. Frequency-doubled or -quadrupled lasers enable shortened wavelength output, but require precise alignment of optical components. Additionally, such lasers are limited to very specific wavelengths, and often operate only in pulsed mode. Other UV lasers, such as excimer lasers, are limited to specific wavelengths, are very bulky and immobile, inefficient and expensive, and also operate only in pulsed mode.
Epitaxial growth of high-quality aluminum gallium nitride (AlGaN) continues to be challenged by a lack of matched substrates. Threading dislocations that result from heteroepitaxy are responsible for leakage currents, trapping effects, and may adversely affect device reliability. AlN nucleation conditions have been determined to be important for reliability of the device when grown on silicon carbide (SiC) substrates.